You can plant rosemary in October if you live in a warm climate. USDA zones 8 through 10 give you enough mild weather for roots to settle in before winter hits. If you live in zones 5 through 7, October planting is risky and you are better off waiting until spring. The key factor is how many weeks of warmth your rosemary gets after you put it in the ground.
When I first tried fall planting, I put two rosemary bushes in the ground in mid-October in my zone 9 garden. The cooler fall air cut down on transplant stress and the plants looked great. They didn't grow as fast as the ones I planted in April though. The shorter days and cooler nights slowed root growth quite a bit. Both bushes made it through winter just fine but the spring-planted ones were twice as big by then.
Fall rosemary planting works because the cooler air puts less strain on new plants. Water doesn't dry out as fast in autumn, so roots stay moist without extra work from you. The soil is still warm from summer heat, which helps roots spread before the cold sets in. These perks make fall a solid choice for growers in warm zones who missed the spring window. You also deal with fewer bugs in autumn, which gives your young plant time to grow strong before pest season starts up again.
Your rosemary needs at least four to six weeks of mild temps above 40°F (4°C) to set roots before it goes dormant for winter. That is the bare minimum. If your area drops below that mark in early November, October is too late to plant. Check your first frost date and count back six weeks. If that lands before your planting day, wait for spring instead.
The Arp variety handles the most cold of any rosemary. University of Maryland data shows it can survive down to -10°F (-23°C) once roots are set. NC State Extension lists zones 8a through 10b as the main range for growing rosemary in the ground year-round. If you are in a colder zone, the rosemary planting season for you starts and ends in spring.
If you live in zones 5 through 7 and still want to start rosemary in fall, use a pot instead of the ground. A 14-inch (35 cm) container lets you bring the plant inside when temps drop below freezing. Set it by your brightest window and cut back on water until spring arrives. Then move it outside once night temps stay above 40°F (4°C) for good.
For any fall rosemary planting, spread two to three inches (5-8 cm) of mulch around the base of the plant. This shields the roots from sudden cold snaps and holds in soil warmth from the day. Don't pile mulch against the stems though, since that traps moisture and can cause rot. Leave a small gap of about an inch between the mulch and the main stem.
October planting can work great for your rosemary if you match the timing to your zone and pick a tough variety. The rosemary planting season is wider than most people think. Warm-zone growers have a real edge in fall. Cold-zone growers do best in spring. Either way, plan ahead and your rosemary will reward you with years of fresh herbs and great scent. In my experience, the extra care you put in during the first six weeks after planting makes all the difference for long-term health.
Read the full article: Rosemary Plant Care and Growing Guide
